Warm Idle Problem

[Hubberth]

85 911 runs well but has idle surge when warm. Vacuum leak? Air flow meter?

[DRACO A5OG]

Check you Idle Control Valve. take a screw driver and tap it when it "HUNTS" if it goes away, Bingo, clean it but if it doesn't go away, check the OHMs to insure it is in tolerances.

After that I would check the Air Fuel Ratio to insure it is in specs and check your Base Idle is set correctly.

Oh yeah Welcome aboard, any pics?

[kidrock]

+1 with Draco. Your dilemma is common with these cars, but generally a simple and inexpensive fix. Hunting idle is usually due to a faltering Idle Control Valve (ICV), a faltering O2 sensor, or a rich mixture in your air/fuel ratio. I'm assuming you recently purchased the car? Purchasing a Bentley manual for these cars is highly recommended, and can be purchased from our BBS host on this site.

Oh, and +1 with the "welcome" and the pics, too.

[stlrj]

If it's a fast hunt, it might be from the base idle speed set too high or an intake gasket vacuum leak.

Cheers,

Joe

[Hubberth]

Thanks for the help. I have replaced the idle control valve next I'll check the air fuel mixture. I've had the car for two years. Here is a photo.

[kidrock]

very nice.

[Venetian]

A new oxygen sensor and air/fuel adjustment solved the same problem for me.

[DRACO A5OG]

Very Nice, so your ICV failed? If that fixed it you should not have to mess with the AFR.

[Hubberth]

HI No the ICV seems fine and I have already changed the oxygen sensor. It idles at about 820, does seem a little rich though. Back to work.

[kidrock]

Hubberth,

how did you check your ICV? If your base idle is 820, that's pretty much in range (800 rpm idle for stock '84-'86, 880 rpm idle for stock '87-'89). If you've replaced your O2 sensor and you know your ICV is good, take a look at your AFM. Draco has good info on this, it seems like he's on the never-ending quest for The Perfect Idle

[Hubberth]

Checked the resistance and it was off by a very small amount so I put in a new one. It didn't seem to change anything. The hole plug on the bottom of the Air Flow Meter is missing so I think someone might have played with it before I got the car. Should I try to adjust it or is it something that has to go to the shop? Neil

[DRACO A5OG]

Hey Neil,

If you are stock 85 then your target RPM's should be 780 per spec. But I have seen people bump it up but the DME will be working overtime to bring the idle back down to 780 per programming.

If cap on the AFM is missing then most likely someone messed with it.

If you have a LM1 (preffered) you can do it yourself then reset your base idle.

No LM1? then you can go ghetto and use a Digital Volt Meter connected to the O2 Sensor to obtain a close to the proper Air Fuel Ratio as circumstances will allow but you still will need to reset your base idle after adjustment.

Kidrock, LOL yeah you are right I am obsessed. I think my next step is to replace my intake manifold gaskets. It is the onlly thing that I have not replaced. I suspect this because once warm she will idle properly but when cold she get's finiky on the idle until I blip her but performs perfectly. If I keep my eyes away from the tach, no issues.

My friends think I am crazy but I don't care I am going to fix it unless it kills me first.

Jim

[kidrock]

Hubberth,

here is an excellent thread on your very same problem. I started on pg.4 so you could learn how simple it is to set your mixture. You'll probably need to lean it out a bit. There's also some helpful tidbits in here about testing your idle microswitch. The entire thread is 8 pages, but it is a wealth of knowledge regarding hunting idles in our 3.2's. Grab a beer, read up a bit and keep us in the loop. You can definitely do this without taking her to the shop.

idle bounce

Draco, LOL I get pumped reading your threads. As soon as you post something, I run out to the garage and start funking around with the same stuff. I should probably thank you, every time I go out there I manage to get that sumbeatch purring a little more.

[Hubberth]

Well it's been a crazy week, but with all your help I now have an 85 911 running like it is supposed to.( Not perfect but with 250000 miles on it, it's really close.) Idle was a little high and it was running rich. Idle is now at 780 and setting for the AFM on the meter is now .625. Also this week I changed the tie rod ends, ball joints, fuel pump and tires. I have to look at the head liner next.
Thanks again Neil

[kidrock]

glad to hear ya got her going in the right direction. Now get out and drive that bad boy!!!

I can't believe that car has 250K on it, really looks great.

[Hubberth]

Just got back from a 500 mile run. I love this car. Ran great the whole time and got about 29 miles a gallon. Thanks again for all the help. Neil